Joints of protective conductors shall be accessible for inspection and testing except m compound-filled or encapsulated joints.  No switching device shall is inserted in the protective conductor, but joints which can bedisconnected for test purposes by use of a tool may be provided.  An auxiliary earth electrode shall be provided electrically' independent of all other earthed metal, forexample, constructional metalwork, pipes, or metal-sheathed cables. This requirement i. consideredto be fulfilled if the auxiliary earth electrode is installed at a specified distance from all other earthedmetal (value of distance under consideration).  The earthing conductor leading to the auxiliary earth electrode shall be isolated to avoid contact withthe protective conductor or any of the parts connected thereto or extraneous conductive parts whichare, or may be, in contact with them.  In TN systems, for cables in fixed installations having a cross sectional area not less than 10mm 2 forcopper and 16mm 2 for aluminum, a single conductor may serve both as protective conductor andneutral conductor, provided that the part of the installation concerned is not protected by a residualcurrent-operated device.  However, the minimum cross sectional area of a PEN conductor may be 4mm 2 , provided that thecable is of a concentric type conforming to Indian Standards and that duplicate continuityconnections exist at all joints and terminations in the run of the concentric conductors.  When the source of energy is privately owned, there should be no metallic connection with theGeneral public supply unless there has been consultation with the electricity authority concerned.  It should be emphasized that an installation together with its source of energy may not consist entirely of one particular type of system. In such cases, each part of that installation may be requiredto be treated separately without detriment to other parts of the same installation.  RCD's having Minimum Operating Currents Greater Than 30 mA -- These devices are intended to giveindirect shock risk protection.  The neutral points of each separate electricity system which has to be earthed at the power station orsubstation.  GI/Copper Plate Size: 500mmX500mmX10mm.  Wood coal powder and salt are in same quantity.  Size of GI Strip: 300mmX10mm  Size of GI Pipe: 2.5" Diameter.  Minimum 1Ω Resistance should be available at a distance of 15mt.  IR value of Earth resistance is less than 10Ω.  Earthing resistance of earthin g rod is changed from 0.3Ω to 0...8Ω between summer to winter.  Distance between two earthing pit is 2 X Length of earthing electrode.  If ground resistance is less than plate earthing (if hard rock) than Pipe earthing shall be used.  Resistance between two earthing pit is negligible.  Earthing of lighting protection should not mix with power system earthing.  Lighting protection earthing should be 10 time stronger than normal earthing (use copper bus stripinstead of wire)  Jointing of earthing strip shall be overlap of min 50mm and for earthing wire overlapping shall bemin 40mm